Fluid-powered, positive-displacement engine

ABSTRACT

A fluid-powered, positive-displacement engine of the type wherein pistons, in annular series arrangement within respective cylinders, act successively on the circumferential margin of a positionally fixed shuttle plate to rotate a power-output shaft to which the plate is rigidly secured, concentrically therewith. There is disclosed a compact and efficient fluid-flow system for both the supply and exhaust of a pressure fluid, such as steam, that provides the power to operate the engine, and a rotary valve operated by the power-output shaft for timing supply and exhaust of pressure fluid progressively around the annular series of cylinders and for effecting reverse operation of the engine. Each piston is formed to straddle the shuttle plate and to, thus, be double acting at respectively opposite sides of such plate. Adjustable low-friction couplings connect the pistons with the shuttle plate.

United States Patent [72] Inventor George D. Eddington 266 East 100South, Logan, Utah 84321 [21] Appl. No. 818,206 [22] Filed Apr. 21, 1969[45] Patented Oct. 19, 1971 [54] FLUID-POWERED,POSITIVE-DISPLACEMENTENGINE 11 Claims, 12 Drawing Figs.

[52] US. Cl 91/502, 91/503, 92/138 [51] Int.Cl .L F01b3/02, F01b 13/04[50] Field of Search 91/175, 501,502, 503; 92/138, 88, 57; 103/173;308/234 [56] References Cited UNITED STATES PATENTS 1,781,068 11/1930Michell 91/175 2,434,747 l/1948 Ruben 91/175 2,997,956 8/1961 Stewart103/173 3,006,324 10/1961 Shaw 91/175 673,220 4/1901 Perkins 308/2341,127,267 2/1915 McElwain 2/138 2,409,868 10/1946 Kahl 92/138 PrimaryExaminer-Paul E. Maslousky Attorney-Mallinckrodt & MallinckrodtABSTRACT: A fluid-powered, positive-displacement engine of the typewherein pistons, in annular series arrangement within respectivecylinders, act successively on the circumferential margin of apositionally fixed shuttle plate to rotate a power-output shaft to whichthe plate is rigidly secured, concentrically therewith. There isdisclosed a compact and efficient fluidflow system for both the supplyand exhaust of a pressure fluid, such as steam, that provides the powerto operate the engine, and a rotary valve operated by the poweroutputshaft for timing supply and exhaust of pressure fluid progressivelyaround the annular series of cylinders and for effecting reverseoperation of the engine. Each piston is formed to straddle the shuttleplate and t0, thus, be double acting at respectively opposite sides ofsuch plate. Adjustable low-friction couplings connect the pistons withthe shuttle plate.

PAIENIEnucr 19 I97! SHEET 2 OF 3 INVENTOR. GEORGE D. EDDINGTON II/ I ATTORNE YS PATENTEDUBT 19 I97! 3,613,511 SHEET 30F 3 PTMX INVENTOR. GEORGED. EDDINGTON ATTORNEYS FLUID-POWERED, POSITIVE-DISPLACEMENT ENGINEBACKGROUND OF THE INVENTION 1. Field The invention is in the field ofpositive displacement engines adapted to be driven by a fluid underpressure, such as steam, and particularly those of the type equippedwith pistons arranged in annular series about the circumferential marginof a wobble or other form of positionally fixed shuttle plate forrotating a drive shaft upon which the plate is mounted.

2. State of the Art Many different forms of the type of engine concernedhave been proposed. Although prototypes of some of these have been builtand operated successfully, so far as applicant is aware none haveachieved any significant degree of commercial success. Examples of thistype of engine are found in U.S.'

Pat. Nos. 3,383,930; 3,370,511; 3,274,897; 3,246,577; 3,120,816;3,082,697; 3,080,854; 3,071,014; Re23,803; 2,157,692; and 1,837,724.

3. Objectives Although the general concept of the engine was old at thetime the invention was made, it was a primary purpose of the inventionto achieve at least as great efficiency of operation as previously, butby a simpler and more compact construction that virtually eliminatesexternal piping and the heat losses incidental thereto; that providesdouble power strokes and balanced operation in the powered reciprocationof each piston; that utilizes adjustable, low-friction couplings betweenthe respective pistons and the shuttle plate, without springs andunaccompanied by backlash; that includes an exhaust system enabling thepressure fluid to be collected and reused; that incorporates a controlvalve as a part of a pressure fluid distribution system of the engine;that provides positive, accurate, and trouble-free timing for allaspects of engine operation; that achives such a timing of piston powerstrokes as neutralizes end-thrusts on the power output shaft of theengine; and that provides for reverse drive in a manner eliminatinggears or other mechanical linkage andpermitting shifting by remotecontrol from forward to reverse and vice versa with the engine stopped,idling or at an operating speed.

SUMMARY OF THE INVENTION The inventive construction comprises elongate,rectilinear pistons, each recessed centrally of its length to receivethe peripheral margin of the shuttle plate intermediate its oppositeends, so that, in operating within opposed, rectilinearly alignedcylinders, each piston becomes double acting and receives power on eachreciprocative stroke. The intermediate, confronting faces of each pistonare advantageously coupled to respective opposite faces of the shuttleplate by adjustable antifriction means, which, in one form, may comprisecombined radial and thrust type of antifriction bearings for respectiveopposite faces of a shuttle plate formed as a cam plate, and, in anotherform, may comprise respective ball and socket couplings and annularbearing race plates for respective opposite faces of a shuttle plateformed as a wobble plate.

The sockets of the balland socket couplings of the latter form ofantifriction means advantageously comprise recessed pads that rest andslide freely on the respective bearing race plates, and recesses incorresponding ones of the confronting intermediate faces of therespective piston end portions. Each end portion of a piston isadvantageously provided with a passage axially thereof, which is open atboth ends-as by making such piston end portion tubular-to receive a rodformed with a ball, or with a ball-receiving socket recess, at theintermediate face that is coupled to the wobble plate. It isadvantageously threaded at the other end for screwing into correspondingthreading provided internally of the outer end of such piston endportion. This enables the seating pressure of the ball within itsreceiving socket to be adjusted as desired.

The control valve is positioned at one end of the power output shaft towhich the shuttle plate is fixedly secured, and includes a rotary valvemember coupled to the power output shaft for rotation therewith and formovement axially of such shaft to shift operation of the engine intoreverse and back into forward drive when desired.

The pressure fluid distribution system and the exhaust system are formedinternally of and closely about the cylinder block, which results in avery compact structure, virtually without outside piping.

THE DRAWINGS Specific constructions presently contemplated as the bestmode of carrying out the invention in actual practice are illustrated inthe accompanying drawings, in which:

FIG. 1 represents one fonn of the engine in longitudinal vertical sectontaken on the line 1-1 of FIGS. 3, 4, and 8, with the control valve inforward-drive position;

FIG. 2, a fragmentary view corresponding to the control valve portion ofFIG. 1, but taken on the line 2-2 of FIG. 9 and showing the valve inreverse-drive position;

FIG. 3, a transverse vertical section taken on the line 3-3 of FIG. 1;

FIG. 4, a similar section taken in the line 4-4 of FIG. 1;

FIG. 5, a similar section taken on the line 5-5 of FIG. 1;

FIG. 6, a fragmentary vertical section taken with respect to the line6-6 of FIG. 4, but not limited axially of the engine;

FIG. 7, a diagrammatic representation of the several cylinders andpistons in operative conjunction with a transverse vertical sectiontaken on the line 7-7 of FIG. 1 to reveal pressure fluid supply portsand passages of the valve in its forwarddrive position and to indicatethe firing" order of the several cylinders;

FIG. 8, a view similar to the sectional portion of FIG. 7, but showing acorresponding transverse vertical section taken on line 8-8 of FIG. 1with respect to the reversing portion of the valve in the forward-driveposition of such valve;

FIG. 9, a view similar to FIG. 8, but taken on the line 9-9, FIG. 2, toshow the positions of the several parts and flow passages of the valvein the reversing position thereof;

FIG. 10, a corresponding view taken on the line 10-10 of FIG. 2;

FIG. 11, an end elevation taken from the right in FIG. I; and

FIG. 12, a view corresponding to an intermediate portion of FIG. 1, butshowing a simplified form of shuttle plate and antifriction couplingsfor the several pistons.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS In the form illustratedin FIGS. 1-10, the engine of the invention comprises a cylinder block 15of cylindrical formation provided with an annular series of individualcylinders [6 surrounding an axially extending bore 17 that receives androtatably mounts a power shaft 18 to be driven by the engine. Mounted onthe shaft 18, as by being formed integrally therewith, is a positionallyfixed shuttle in the form of a wobble plate 19. The cylinder block 15 isannularly recessed internally thereof and intennediate its ends,transversely of the several cylinders 16, as at 20, to accommodate thecircumferential margin of the wobble plate 19; antifriction bearings 21serve to journal the shaft 18 for rotation relative to the cylinderblock.

Slidably mounted for reciprocation in the cylinders 16 are respective,elongate pistons 22, each recessed intermediate its length, as at 23,for receiving and straddling the circumferential margin of the wobbleplate 19. As shown, such pistons'are tubular, for adjustably receivingrods 24. They are shown provided with respective piston rings 25, butmay, if desired, be provided with elongate sleeve bushings (not 1 shown)externally of their opposite end portions.

posite faces of wobble plate 19 by antifriction bearings 27 and 28 ofring formation. As so mounted, the wobble plate is free to rotaterelatively to the pistons and the couplings with a minimum amount offrictional resistance.

In the form illustrated, the ball and socket couplings each compriseball means at the intermediate face of the corresponding piston endportion 22a and a free-sliding pad 29 on the corresponding race plate26, the pad having a socket recess formed therein for receiving the ballmeans. Although the ball means may be formed in various ways, as bymaking the appropriate end of the rod 24 hemispherical, it is preferredto recess such end of rod 24 as a ball-receiving socket and to provide afreely rotatable ball 30 fitted between the mutually opposing socketrecesses.

The rods 24 are preferably adjustably mounted in their respective pistonend portions 22a by screw-threading 31 at the opposite ends of such rodsand at the outer ends of the piston end portions. This permits theposition of each rod 24 to be adjusted axially along the correspondingpiston end portion to regulate the degree of tightness of the ball 30within its socket recesses and to take up any wear that might occur. Thesame arrangement could be used, of course, in instances of the rod endbeing made hemispherical as the ball member of the ball and socketcoupling.

Cylinder heads are provided at opposite ends of cylinder block by setsof annular disks 32 and 33, at one end, and 34 and 35 at the other.These serve to close, and, by means of respective sets of interposedgaskets 36, 37, 38, and 39 to seal the cylinders 16 against fluidleakage. They also serve to supply pressure fluid to the severalcylinders by way of passages formed in such cylinder heads andconstituting part of the pressure fluid distribution system.

The pressure fluid distribution system includes a rotary valve,indicated generally at 40, that comprises a stationary valve body 41 ofannular formation and an axially shiftable, rotary valve member 42operable within the valve body. Pressure fluid, such as steam suppliedform any suitable source under the control for a quantity control valve(not shown) to govern engine speed, is introduced by piping (not shown)to a forward-drive inlet passage 43, FIG. 1, that is formed through anipple fitting 44 in stationary valve body 41.

For forward drive, such pressure fluid flows through axial passage 45,FIGS. 1 and 7, radial passage 46, and arcuate distribution port 460 (allin rotary valve member 42) and, progressively, into radial portions 47aof individual passages 47 of a circular series of such passages in thestationary valve body 41 as such valve member rotates. The passages 47have longitudinal portions 47b that connect, by way of respectivepassages 48, FIG. 5, in cylinder head disk 35, with distributionpassages 49, 50, 51, 52, 53, and 54, respectively, also in such disk 35.Each distribution passage provides for simultaneous supply of thepressure fluid to opposite ends, respectively, of a pair ofdiametrically opposite cylinders 16, whereby wobble plate 19 is drivenby equal and opposite forces applied, respectively, at diametricallyopposite points on its circumferential margin, progressivelytherearound. For this purpose, cylinder head disk 34 is provided with aseries of passages 55, FIG. 1, leading into the corresponding ends ofrespective cylinders 16, cylinder head disk 32 at the opposite end ofthe cylinder block is provided with distribution passages 56, 57, 58,59, 60, and 61, FIG. 4, its companion cylinder head disk 33 is providedwith a series of passages 62, FIG. 1, leading into the correspondingends of respective cylinders 16, and a circumferential series oflongitudinal distribution passages 63, FIG. 3, are provided from end toend of cylinder block 15.

Exhaust from opposite end portions of each of the cylinders 16 isaccomplished primarily through respective ports 64, FIG. 1. Escape offluid from each cylinder during the return stroke of the piston thereinto avoid needless compression of such fluid and reduced efficiency ofengine operation is accomplished primarily through the same passagesthat supply the pressure fluid. Thus, the pressure stroke of each piston22 serves to exhaust residual fluid from the opposite end potion of thecylinder 16 concerned. For this purpose, valve body 41 is providedwithin exhaust passage 65, FIGS. 1 and 10, and rotary valve member 42 isprovided with an arcuate distribution port 66, FIGS. 1 and 10, thatestablishes exhaust communication of the several distribution passagespreviously described with passage 65 by reason of the fact that valvemember 42 is in the axially forward position of FIG. 1.

Cylinder head disks 32 and 33 and their interposed gaskets 36 and 37 areheld tightly over the open cylinder ends at the one end of cylinderblock 15 by a series of bolts 67, FIGS. 3, 4, and 6. Cylinder head disks34 and 35 with their interposed gaskets 38 and 39, together with valve40 and an interposed gasket 68, are held tightly over the open cylinderends at the other end of cylinder block 15 by a series of bolts 69,FIGS. 5 and 11. It is convenient to make cylinder block 15 in twocylindrical sections 15a and 1512, as shown in FIG. I, with aninterposed gasket 70. Bolts 67 are long enough to pass entirely throughthe one section 1511 and to screw into the other section 15b, so as tohold the entire assembly securely together. Bolts 69 need only be longenough to screw into the adjacent cylinder block section 15b.

The assembly, as so secured, is advantageously enclosed by a cylindricaljacket 71, FIG. 1, that is recessed circumferentially internally toprovide an elongate, annular exhaust manifold 72 into which the exhaustports 64 open. Such manifold intersects exhaust passage 65, FIG. 10, invalve body 41, see FIG. 10, and both manifold and passage discharge toatmosphere through a port 74 in jacket 71. For sealing against escape ofexhaust otherwise than through port 74, O-ring gaskets 75, FIG. I, areinterposed between jacket 71 and the cylindrical assembly, an end plate76 being provided at the power-output end 18a of shaft 18 and secured inplace by screws 77, and a retainer ring 78 being secured in place at theopposite end of the assembly by screws 79.

Rotary valve member 42 is coupled to power shaft 18 to be driventhereby. For this purpose it is provided with a stem 42a that ispolygonal in cross section and is received by a correspondingly elongateand polygonal recess in the adjacent end of shaft 18 for back and forthsliding movement axially of the shaft, thereby permitting the valvemember to be shifted axially without uncoupling it from the shaft.

Reverse drive is achieved by axially shifting rotary valve member 42from the forward-drive position of FIG. 1 to the reverse-drive positionof FIG. 2. This is accomplished by introducing a reversing pressurefluid, preferably from the same source as the drive pressure fluid,under the control of a reversing valve (not shown) and through suitablepiping connected to port 80, FIGS. 1 and 11. A passage 81, FIG. 1,conducts such pressure fluid to the forward face of rotary valve member42 and shifts such valve member backwardly along the axis of the engineagainst the force of the incoming drive pressure fluid and of acompression spring 82.

In the shifted position of FIG. 2, see also FIG. 9, pressure fluidentering passage 45 of rotary valve member 42 through inlet port 43 ofbushing 44 flows through radial passage 83 and arcuate distribution port84 into the corresponding flow passages (47a, 47b, 48, etc.) of thedistribution system. It should be noted that the arcuate port 84 extendscircumferentially of rotary valve member 42 in a direction opposite tothat in which arcuate distribution port 46a extends, thereby supplyingthe pressure fluid in a manner to rotate wobble plate 19 and power shaft18 in reverse.

During this reverse operation of the engine, the residual fluid escapesfrom the several cylinders 16 by way of the distribution passagesaforedescribed, arcuate distribution port 66, FIGS. 2 and 10, a port 85,and an annular bypass groove 86 that is in open communication withexhaust passage 65.

FOr fluid-sealing purposes O-rings 87, FIG. 2, are interposed betweenrotary valve member 42 and the stationary structure against which itboth rotates and slides axially.

In order to adjust the axial position of rotary valve member 42 relativeto its stationary valve body 4I, a screw 88 may be threaded in the endof valve stem 42a and adjusted in position from time to time as may befound desirable.

A body of lubricant, such as motoroil, is introduced into the enginethrough an externally available port, such as is provided by an ordinaryoil fitting 89, FIG. 1, and serves to lubricate all working parts duringoperation. Fitting 89 extends through jacket 71 and the adjacent wall ofcylinder block to a discharge termination at an oil passage 90 providedby a circumferential recess in the uppermost piston 22. The lubricantmakes its way to valve 40 through a passage 91 in power shaft 18,through a registering passage in adjustment screw 88, and through apassage 92 along the stem and in the body of rotary valve member 42.

The firing" order, i.e. the power strokes of the several pistons 22, areindicated in FIG. 7, along with the exhaust strikes. The severalcylinders and pistons are designated by the numbers 1-6 respectively.The designation Pr indicates pressure, while the designation Ex"indicates exhaust. The directions of the respective piston strokes andfluid flows are indicated by appended arrows. Similar cylinder andpiston designations, numbers 1-6 as applied to FIGS. 4 and 5, indicatefluid flow through the distribution and exhaust system in correspondencewith the showing of FIG. 7.

The embodiment of FIG. 12 is similar in all respects to that of FIGS.1-11, except for the nature of the positionally fixed shuttle and theantifriction coupling means. In FlG. 12, such shuttle takes the form ofa cam plate 93 presenting circular tracks 94, respectively, that aremutually parallel but eccentric within the planes of their respectivecircles. The antifriction coupling means between the respective pistons95 and cam plate 93 are antifriction bearings 96 of a type knowncommercially as combined radial and thrust needle bearings and readilyobtainable on the open market, as, for example, those manufactured byGarlock-Nadella, lnc., Cherry Hill, New Jersey, as Type RAX. The onlyalteration required is to replace the outer race ring thereof with arace ring 96a having an appropriately sloping face 97, as illustrated.

The bearings 96 are mounted on respective pins 98, headed at one end, asat 98a, to insure retention in countersunk bore holes 99 that areprovided in each of the opposite end portions of the respective pistons95.

In order to provide for the takeup of slack caused by wear, it isdesirable that each piston 95 be divided at its midpoint to make each ofthe opposite end portions thereof a separate and independent unit, andthat these units be adjustably joined together, as by means of a bolt100 passing freely through one of the parts and threaded into the otherpart. Other means of adjustably interconnecting the component pistonunits could, of course, be employed.

Whereas presently preferred embodiments of the invention are illustratedand described in detail, it should be understood that the inventionconcepts permit of various changes in construction.

lclaim:

1. ln fluid-powered, positive-displacement engine of the type whereinpistons, within respective cylinders and in annular series arrangement,act successively on a circumferential margin of a positionally fixedshuttle plate to rotate a poweroutput shaft to which the shuttle plateis rigidly secured, axially thereof, a pressure fluid distributionsystem including a control valve, having a stationary valve body andhaving a rotary valve member coupled to the power-output shaft forrotation therewith and for movement axially thereof to shift operationof the engine between forward and reverse drives; and wherein means areprovided for moving said rotary valve member back and forth axially toshift operation of the engine.

2. ln a fluid-powered, positive-displacement engine of the type whereinpistons, within respective cylinders and in annular series arrangement,act successively on a circumferential margin of a positionally fixedwobble plate to rotate a poweroutput shaft to which said wobble plate isrigidly-secured, axially thereof, the improvement according to claim 14comprisingrace plates at respectively opposite faces of said wobbleplate; ball and socket couplings between said pistons and said raceplates, said couplings each comprising ball means at the piston facethat confronts the correspondin race plate and a rec-sliding pad on saidrace plate, said pa having a socket recess formed therein and said ballmeans being received by said socket recess.

3. The improvement set forth in claim 2 wherein the ball portion of eachcoupling is a freely rotatable ball; wherein each piston end portion istubular and is adjustably fitted with an axially movable rod in thehollow interior thereof, one end of which is recessed to provide asocket for said ball; and wherein means are provided for adjustablysecuring the other end of said rod to said piston end portion.

4. In a fluid-powered, positive-displacement engine of the type whereinpistons, within respective cylinders and in annular series arrangement,act successively on the circumferential margin of a positionally fixedshuttle plate to rotate a poweroutput shaft to which the shuttle plateis rigidly secured, axially thereof, the improvement according to claim14 characterized by the shuttle plate being of cam formation and theprovision of combined radial and thrust-type antifriction bearingscarried by the respective pistons and being interposed between said camformation and the confronting faces of said pistons, the said bearingseach including a mounting pin mounted in the corresponding piston, arace ring, and antifriction means mounting the race ring concentricallyon said pin so its outer circumferential face rides against said camformation.

5. An improvement in accordance with claim 4, wherein each mounting pinis headed at one end and fitted freely through a receiving aperture inthe piston so as to be retained by said headed end, the race ring andantifriction means being freely mounted on the opposite end of said pinso as to be retained in position by the shuttle plate.

6. An improvement in accordance with claim 5, wherein the pistons areeach one part of a double-acting piston that straddles the shuttleplate, each of the double-acting pistons comprising two piston partsadjustably secured together in end-toend relationship.

7. The improvement set forth in claim 1, wherein the cylinders areformed in a cylindrical cylinder block and are closed by cylinder headsat respective opposite ends of the block, and the pressure fluiddistribution system is formed in said cylinder block and cylinder heads.

8. The improvement set forth in claim 7, wherein the cylinder heads areprovided by respective sets of end disks of substantially the samediameter as the cylinder block, and wherein fluid flow passages areformed between the disks of each set.

9. The improvement set forth in claim 7, wherein the valve body of thecontrol valve is formed as an end disk of substantially the samediameter as the cylinder block and cylinder heads.

10. The improvement set forth in claim 9, wherein a cylindrical jacketclosely encompasses the cylinder block, the cylinder heads, and thevalve, and provides an elongate annular fluid-flow passage forconducting exhaust from the cylinders, said cylinders being providedwith exhaust ports leading into said exhaust passage.

11. The improvement set forth in claim 1, wherein the means for movingthe rotary valve member axially comprise fluid-flow passage meansextending from a location of pressure fluid access to the end of saidvalve member that is opposite the pressure fluid input end of thecontrol valve.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent3,613,511 Dated October 19, 1971 Inventor (1:) George D. Eddington It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

r- Column 6, Line 2, change "14" to --1-.

Column 6, Line 22, change "14" to 1-.

Signed and sealed this 21st day of Mar-ch 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTI'SCHALK Attesting Officer-Commissionerof Patents

1. In fluid-powered, positive-displacement engine of the type whereinpistons, within respective cylinders and in annular series arrangement,act successively on a circumferential margin of a positionally fixedshuttle plate to rotate a power-output shaft to which the shuttle plateis rigidly secured, axially thereof, a pressure fluid distributionsystem including a control valve, having a stationary valve body andhaving a rotary valve member coupled to the power-output shaft forrotation therewith and for movement axially thereof to shift operationof the engine between forward and reverse drives; and wherein means areprovided for moving said rotary valve member back and forth axially toshift operation of the engine.
 2. In a fluid-powered,positive-displacement engine of the type wherein pistons, withinrespective cylinders and in annular series arrangement, act successivelyon a circumferential margin of a positionally fixed wobble plate torotate a power-output shaft to which said wobble plate is rigidlysecured, axially thereof, the improvement according to claim 14comprising race plates at respectively opposite faces of said wobbleplate; ball and socket couplings between said pistons and said raceplates, said couplings each comprising ball means at the piston facethat confronts the corresponding race plate and a free-sliding pad onsaid race plate, said pad having a socket recess formed therein and saidball means being received by said socket recess.
 3. The improvement setforth in claim 2 wherein the ball portion of each coupling is a freelyrotatable ball; wherein each piston end portion is tubular and isadjustably fitted with an axially movable rod in the hollow interiorthereof, one end of which is recessed to provide a socket for said ball;and wherein means are provided for adjustably securing the other end ofsaid rod to said piston end portion.
 4. In a fluid-powered,positive-displacement engine of the type wherein pistons, withinrespective cylinders and in annular series arrangement, act successivelyon the circumferential margin of a positionally fixed shuttle plate torotate a power-output shaft to which the shuttle plate is rigidlysecured, axially thereof, the improvement according to claim 14characterized by the shuttle plate being of cam formation and theprovision of combined radial and thrust-type antifriction bearingscarried by the respective pistons and being interposed between said camformation and the confronting faces of said pistons, the said bearingseach including a mounting pin mounted in the corresponding piston, arace ring, and antifriction means mounting the race ring concentricallyon said pin so its outer circumferential face rides against said camformation.
 5. An improvement in accordance with claim 4, wherein eachmounting pin is headed at one end and fitted freely through a receivingaperture in the piston so as to be retained by said headed end, the racering and antifriction means being freely mounted on the opposite end ofsaid pin so as to be retained in position by the shuttle plate.
 6. Animprovement in accordance with claim 5, wherein the pistons are each onepart of a double-acting piston that straddles the shuttle plate, each ofthe double-acting pistons comprising two piston parts adjustably securedtogether in end-to-end relationship.
 7. The improvement set forth inclaim 1, wherein the cylinders are formed in a cylindrical cylinderblock and are closed by cylinder heads at respective opposite ends ofthe block, and the pressure fluid distribution system is formed in saidcylinder block and cylinder heads.
 8. The improvement set forth in claim7, wherein the cylinder heads are provided by respective sets of enddisks of substantially the same diameter as the cylinder block, andwherein fluid flow passages are formed between the disks of each set. 9.The improvement set forth in claim 7, wherein the valve body of thecontrol valve is formed as an end disk of substantially the samediameter as the cylinder block and cylinder heads.
 10. The improvementset forth in claim 9, wherein a cylindrical jacket closely encompassesthe cylinder block, the cylinder heads, and the valve, and provides anelongate annular fluid-flow passage for conducting exhaust from thecylinders, said cylinders being provided with exhaust ports leading intosaid exhaust passage.
 11. The improvement set forth in claim 1, whereinthe means for moving the rotary valve member axially comprise fluid-flowpassage means extending from a location of pressure fluid access to theend of said valve member that is opposite the pressure fluid input endof the control valve.